What are the requirements for renewing a Non-immigrant OX visa in Thailand, especially regarding funds?

I've never heard of anyone successfully extending (not renewing) a non-OX visa in order to get the second 5 years. I've read reports of people that tried, including bringing everything that immigration should require to do so. But they were told that it wasn't possible.

If you are going to try, the money must be in a Thai bank account, in liquid cash.

You need to go to your immigration office to ask for the specific requirements. I believe it's 3 million baht but you'll want to check for yourself what your office requires. Expect to be rejected though.

I'm assuming you're Australian. Most people just go back to Australia and get a new non-OX using money in their home bank account, since the one consulate in Australia is the only one in the world Thai allows that. So Australians are the only one who use this visa.